Profile board or profile sheets are spaced apart double-walled boards of plastic or metal which are kept a fixed distance apart by webs that connect the walls. The presence of the webs define a plurality of passages or channels between the boards through which a fluid may flow. An example of the use of profile board and further details of its construction are disclosed in Daniel A. Sherwood, U.S. Pat. No. 4,898,153, incorporated herein by reference.
Heat exchangers have been made from profile board. The boards are stacked in spaced apart relationship by spacers which separate adjacent boards. The space between adjacent boards provides a flow path for a heat exchange fluid.
Such heat exchangers are designed to exchange heat between two gas streams that flow perpendicular to each other. A first gas stream flows through the internal passages within the profile board and a second gas stream flows through the passages that are formed between adjacent spaced apart profile boards. Each end of the profile board is open so that the gas stream enters the internal passages through one end of the profile board and leaves the profile board through the opposed end.
Heat exchangers currently made from profile board suffer from several disadvantages. First, such heat exchangers require the respective fluid streams to flow in perpendicular relationship to each other. This arrangement can reduce the efficiency by which heat can be exchanged in some applications. Second, it is difficult and more costly to isolate the respective heat exchanging fluid streams because leakage can occur at the corner seals of the stack of plates. While some heat exchange applications can tolerate some intermixing of the fluid streams (e.g. ventilators in buildings) many applications cannot effectively function in this manner.
Industrial plate-type heat exchangers made without profile board are made from stacks of parallel plates. The plates are made with cut-outs at their respective ends so that internal manifolds are formed when the plates are stacked together. Pipe stubs through which the fluid enters and exits the heat exchanger are attached perpendicularly to the plates at either the front or back of the plate stacks.
These industrial type heat exchangers are disadvantageous because the fluids require complicated gasket and/or seal configurations to isolate the respective heat exchange fluids. In addition single-wall plates customarily used in such industrial-type heat exchangers have a less rigid structure than the profile board and can become misshapen when exposed to different pressures created by the respective fluids. To overcome this problem, the plates of industrial plate heat exchangers are made more rigid (e.g. by stamping them with a pattern of ribs or corrugations).
To the contrary, the webs in the profile board can support tensile loads locally. Thus, if one fluid stream is at relatively high pressure, the profile board heat exchanger could be circuited with this stream within the profile board. The relatively high forces operating to separate the plates would be supported by the webs. In industrial type plate exchangers, these loads are typically supported with heavy end plates linked together with tie bars.
It should be further noted that increasing the thickness of the plate walls is not desirable when the heat exchanger is constructed of plastic. Since plastics have low thermal conductivity, the walls of the heat exchanger must be as thin as possible if a high degree of thermal effectiveness is desired.
Thus, current heat exchangers are deficient because they require complex gaskets and/or seals to prevent intermixing and are typically made of stiff materials, having a high bending modulus so that the plates won't bend under high pressure loads. Stainless steel is an example of a suitable stiff material.
It would therefore be a significant advance in the art of manufacturing heat exchangers to provide a heat exchange device that can maintain the respective heat exchange fluids separate from each other and that can be constructed effectively from low-cost corrosion-resistant materials in a configuration employing relatively thin walls and reduced spacing between the walls.